A vegetarian diet can be successfully followed by those with Crohn's disease (CD) or ulcerative colitis (UC) although more care will be needed to ensure nutritional adequacy and some may find their symptoms are aggravated by foods used to replace meat. Dietary treatment of CD requires very careful planning if foods are to be excluded on top of an already restricted diet.
Some vegetarian diets are stricter than others. The most common form avoids all meat and fish but allows milk, milk products and eggs. A vegan diet excludes all foods of animal origin and is therefore based solely on cereals, cereal products, pulses, vegetables, fruit, nuts and seeds.
Vegetarian and especially vegan diets may be less energy-dense than omnivorous diets because most plant foods contain more water and fibre and less fat than foods of animal origin. Those with problems maintaining weight need to eat more energy-dense foods such as milk and dairy products or soya milk and soya products, and include plenty of starchy foods such as potato, bread, rice and pasta. Nuts, seeds, pulses and dried fruit should be included if these are tolerated.
The protein quality of vegetarian diets should also be considered. A good mixture of plant protein is required to supply all the building blocks (or amino acids) required for growth and tissue repair. This means that over the course of a day, a combination of grains, pulses, nuts, seeds and soya should be included in the vegan diet, with the addition of eggs, milk and dairy products in the vegetarian diet. High energy supplements are usually based on milk protein, although elemental diets contain artificially synthesised amino acids.
Vegetarian diets tend to be high in fibre. This increases the bulk of the diet and may suppress appetite for more energy-rich foods with the risk of weight loss. Also, some high fibre foods such as nuts, seeds, wholegrain cereals, pulses and dried fruit may irritate the gut wall as discussed previously. These foods are rich in substances that bind with minerals in the diet and reduce their absorption in the intestine. It may therefore be necessary to replace some of these high fibre foods with more refined cereal products such as white bread and lower fibre breakfast cereals, and with fruits and vegetables with lower fibre content.
Certain vitamins and minerals may be at risk of depletion, especially in vegan diets. Vitamin B12 is only found in products derived from animals. Some foods such as yeast extract, soya milks and breakfast cereals are fortified with Vitamin B12 and these should be included regularly in the diet, or a Vitamin supplement taken.
The richest source of iron is red meat. Absorption of this mineral may be reduced by fibre and other plant substances. On the other hand, Vitamin C found in fruit and vegetables, especially citrus fruit, improves absorption of iron. Rich plant sources of iron, for example dark green vegetables, soya, pulses, seeds, dried fruit and fortified breakfast cereals, should therefore be eaten with a good source of Vitamin C. An iron supplement may be needed if blood tests indicate anaemia.
Calcium intake may be low on a vegan diet as the best source of this mineral is milk and dairy products. Non-dairy calcium rich foods such as fortified soya products, pulses, nuts, seeds and white bread should be taken regularly but if these foods are not well tolerated, a calcium supplement will be required. If there is concern about the nutritional adequacy of the diet, a dietitian should be consulted. Children, adolescents, pregnant or lactating women and the elderly will have increased nutritional requirements and this requires special attention.